Metric-Palatini gravity unifying local constraints and late-time cosmic acceleration

TL;DR

This paper introduces a modified gravity theory combining Palatini f(R) terms with Einstein-Hilbert action, capable of explaining cosmic acceleration and galactic dynamics while satisfying Solar System constraints.

Contribution

It develops a scalar-tensor representation of Palatini f(R) gravity that remains consistent with local tests and explains late-time cosmic acceleration.

Findings

Theory passes Solar System constraints with a light scalar field.

Models exhibit late-time cosmic acceleration.

No instabilities found in perturbations.

Abstract

We present a novel approach to modified theories of gravity that consists of adding to the Einstein-Hilbert Lagrangian an f(R) term constructed a la Palatini. Using the respective dynamically equivalent scalar-tensor representation, we show that the theory can pass the Solar System observational constraints even if the scalar field is very light. This implies the existence of a long-range scalar field, which is able to modify the cosmological and galactic dynamics, but leaves the Solar System unaffected. We also verify the absence of instabilities in perturbations and provide explicit models which are consistent with local tests and lead to the late-time cosmic acceleration.